One of the attackers at the parliament was arrested, added the news agency, but it is not clear if the other three are still at large and there have been unconfirmed reports of a hostage situation.
State TV later said four attackers took part in the parliament attack, and that eight people were wounded. An apparently coordinated attack took place at the mausoleum of Iranian revolutionary founder Ruhollah Khomeini, several news agencies said.
The latter cited reports of two assailants being arrested at the site.
Gunmen have reportedly opened fire inside Iran's parliament building and at the Khomeini Shrine in Tehran.
FarsNews Agency reported that one of gunmen inside Parliament is a suicide bomber, now surrounded by security forces.
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But the BBC reported that only one security guard was killed in Parliament. One of the attackers on Iran's parliament complex blew himself up on the fourth floor amid an ongoing siege, state broadcaster IRIB reported.
At least seven people were killed and 35 others injured in the twin assaults, the semi-official Fars agency reported.
According to Tasnim dispatches, the gunmen attacked the mausoleum of Imam Khomeini, and fired at people.
A security guard is said to have been killed. Iran has also come under attack in the past by Arab insurgents.
The BBC said this was the most serious terrorist incident in Tehran since the early years of the Islamic revolution of 1979 led by Khomeini.